Composite signaling system



H. S. OSBORNE AND R. D. PARKER.

COMPOSITE SIGNALING SYSTEM.

APPLICATION FILED DEC. 11, I9I8.

1,361,486, Patented Dec. 7, 1920.

Inventors Jttorney UNITED STATES PATENT OFFICE.

HAROLD s. osEoENE, OF NEW YORK, A D EALzEMoNn n. PARKER, or BROOKLYN,

NEW YonK, ASSIGNORS 'ro AMERICAN TELEPHONE AND TELEGRAPH GOM- PANY, ACORPORATION or NEW YORK.

coiviPosrrE SIGNALING SYSTEM.

Application filed December 11, 1918.

1 '0 all whom it may concern:

Be it known that we; HAROLD S. OSBORNE and RALZEMOND D. PARKER, residingat New York and Brooklyn, respectively, in the counties of New York andKings respectively, and State of New York, have invented certainImprovements in Composite Signaling Systems, of which the following isaspecification.

This invention relates to composite signal transmitting systems such,for instance, as are used for simultaneously sending telephone andtelegraph messages over the same wires. Its object is to improve theefficiency of such systems and to render such service available overcircuits of certain characters where it has heretofore beenimpossible.

It has long been common practice to simultaneously transmit telephoneand telegraph messages over the same wires. In the past, however, thetelephone circuits so used have in general had a rclatively small numberof loading coils. The actual use of such compositesystems hasfurthermore been limited to cases in which the telegraph was used with aground return; 7

Telephone currents are of the order of one inilli-ampere while telegraphcurrents 'areordinarily of the order of eighty milli-amperes. It hasbeen found that when telegraph currents of this magnitude aresuperimposed on high eiliciency telephone lines embodying many loadingcoils and the amplifiers now inuse,"tl1at the telephone current isinterfered with to such an extent as to render it unlit for commercialpurposes in some cases wholly unintelligible. This is particularly trueof very long cable circuits in which the total number of loading coilsis large and the amplifiers are operated with very large amplifications.

The undesirable effect upon the telephone current is due primarily tothe effect of the relatively large telegraph currents on. thepermeability of the iron cores of the loading coils resulting in a verygreat change in their apparent resistance to the telephone currents.Also the higher harmonics of the telegraph impulses when magnified bythe high power amplifiers now in use affect the telephone circuit ifthese harmonics are not kept very small in magnitude. In accordance withthis invention, it is proposed to overcome these diliiculties by firstreducing the Specification of Letters Patent.

Patented Dec. 7, 1920;

Serial No. 266,326.

magnitude of the telegraph currents to the order of the telephonecurrents or even less .and then by employing a complete metallic thehigh frequency components of the telegraph iinpulsesin order to avoidinterference with telephone communication. This means that the telegraphcurrent will come to its operating value at a comparatively slow rateand the speed of signaling is necessarily limited. By using a metalliccircuit for the combined telephone and telegraph circuit and reducingthe value of the telegraph current as above indicated, the danger ofinterference with the telephone circuit by the high frequency componentsof the telegraph impulses is so diminished that it is possible to use acomposite set designed to pass a telegraph current wave reaching itsoperating value sooner than under the old system, and therefore givingincreased speeds of operation without interference with the telephoneconversa lion. An advantage also arises from the fact that the telegraphcurrents of a single telegraph circuit pass through both windings of theloading coils 'of the telephone lines instead of through one windingonly as in the grounded circuit, since at the higher speeds of signalingthe loading coils will then be an advantage as in telephonecommunication, instead of detriment.

The invention will be more fully understood by reference to theaccompanying drawings in which Figure 1 is a reproduction from. anoscillograph record showing the interference of telegraph impulses withtelephone currents and Fig. 2 shows diagramm'atically a circuit such asmay be used in employing the present invention.

In Fig. 1, A represents a telegraph current and B the telephone currentas it is affected graph lines the telephone line is provided by theloading coils in the circuit, when a telegraph current A of themagnitude heretofore used is superposed on the circuit. For the purposeof illustration the telephone current is here represented as of aconstant frequency of 800 cycles. It will be noted that there is adiminution of telephone current each time there is a rapid change in thevalue of the telegraph current as at the points 00, each of theseproducing its well identified effect in B at points y. The resultsevidenced at y lag slightly behind the points of rapid change in thetelegraph current as will be seen from the drawing. This diminution isknown as the flutter effect on the telephone circuit and is caused bythe action of the telegraph currents upon the loading coils. This effectmay be so great in some cases as to practically suppress the telephonecurrent.

Referring to',Fig. 2, 1 represents a typical telephone circuit embodyingloading coils 2 and repeaters 3. At each end of the circuit isrepresented a telephone set 44, for sending and receiving telephonemessages and a telegraph apparatus, 55, for sending and receivingtelegraphic signals. The telephone apparatus illustrated is of a wellknown type and needs no detailed description. In the telegraph sets 6represents the receiving relay and 7 in sending key. Each of these is inpractice associated in a well known manner with the usual relays, (notshown).

At the juncture of the telephone and telewith series capacities 8 andshunt induc tance 9 and the telegraph line with series inductanees l0and shunt capacity 11, which serve to prevent the telephone impulsesfrom entering the branch leading to the telegraph instruments and thetelegraph cur rents from entering the branch leading to the telephoneinstruments.

The elements of this composite set 'located in the telegraph branchwill, in accordance with this invention, be designed to permit thepassage of frequencies corresponding to the increased rate of telegraphsignaling which as above noted is possible with the arrangement hereindescribed without interference with the telephone communication. Thewindings of relay 6 are divided between the opposite sides of thecircuit and are connected between the line 1 and the artificial line N.The sending apparatus 7 is connected to the opposite sides of the lineat the midpoints of the relay winding 6 so that impulses emanatingtherefrom will have no eilect upon the -re ceiving relay since theydivide equally and traverse in opposite directions the two halves of thewinding. The groupof series inductances and shunt capacities indicatedat 12 serve to partially suppress the high freitsra'pidly varyingcomponents without interfe'rence with the telephone circuit.

It will be apparent then that the invention herein'describedbeneficially affects both the telephone and the telegraph transmissionin a composite system, in that it removes defects which. the telegraphcurrent introduces in the telephone transmission under present practiceand at the same time increases the speed and reliability of thetelegraph transmission.

' The nature of the invention and the manner of operation will be clear.trom the foregoing without further description. It will be understoodthat the circuit here shown is illustrative only, as the invention maybe employed with a wide variety of circuit arrangements within thespiritof the invention and the scope of the appended claims.

What is claimed is:

. 1. The improvement in the art of composite telephony and telegraphywhich consists in producing telephone signaling currents of the usualcharacter, producing telegraph signaling currents so proportioned as tobe of the same order of magnitude as the telephone currents, orsmaller,and concurrently transmitting said telephone and telegraph currents overthe same pair of conductors.

2. The improvement in the art of com posite telephony and telegraphywhich consists in proportioning the constants of a pair of conductors toeflic'iently promote the propagation of telephone currents producingtelephone signaling currents, and imposing them upon said conductors,and producing telegraph currents so proportioned to said telephonecurrents as to be or, the

currents over the same pair of conductors,

and amplifying said telegraph currents at one or more points on theline.

4. The improvement in the art of composite signaling which consists inproducing telephone and telegraph signaling currents so proportionedasto be of the same order of magnitude, and concurrently transmit-' tingsaid signaling currents over the same pair of conductors, and separatingthe telephone and telegraph currents into separate channels at thereceiving stations.

5. The improvement inthe art of composite signaling Which consistsinproducing telephone currents of the order of five milliamperes,producing telegraph currents of the same order of magnitude, or smaller,and concurrently transmitting said telephone and telegraph currents overthe same complete metallic circuit.

6. The improvement in the art of composite signaling Which consists inproducing telephone signaling currents of the usual order of magnitude,producing telegraph currents of the same order of magnitude, or smaller,imposing said telephone and telegraph currents upon the same pair ofconductors, and increasing the sending rate of the telegraph signals toa point above that possible With usual telegraph currents of the orderof 80 milliamperes, and to a degree sufficient to profit by thecharacteristics of the conductors designed to efiiciently propagate thetelephone currents.

In testimony whereof We have signed our names to this specification thisninth day of December, 1918.

HAROLD S. OSBORNE. RALZEMOND D. PARKER.

